The present invention relates to ribbon drive systems and more particularly to a drive system for the ink ribbon in a data printer of the type having a bidirectionally movable print heat carriage upon which is mounted a ribbon cartridge.
Various forms of data printers are presently available and which are primarily used to produce printed copy as readout from computer systems. One such printer is commonly referred to as a dot matrix impact printer. This printer includes a carriage supported, multiple-stylus print head which impacts its style against an ink ribbon positioned in front of the paper to be printed. A resilient platen is disposed behind the paper. The carriage and print head are supported on a lead screw drive shaft and a guide or slide rod arrangement in front of the platen. The printer also includes a paper advance mechanism and a logically controlled actuation system. The actuation system causes the carriage and print head to reciprocate bi-directionally across the paper. Such printers have the capability of printing in both directions as the carriage is translated by alternating the direction of rotation of the lead screw drive.
Typically, with printers employing a carriage mounted print head, the inking ribbon is supported directly on the carriage. The ribbon is typically contained in a cartridge and is looped around suitable guides in front of the print head. Provision must be made for driving the inking ribbon.
Various systems have been proposed for mounting and driving the inking ribbon in this type of printer. An example of one such system employs a ribbon cartridge having a supply spool and a takeup spool. The drive mechanism is a fairly delicate pawl and ratchet device and the takeup spool is driven while the carriage translates in one direction only. This arrangement could result in imperfect printing or character definition since the same area of the ink ribbon is struck while the carriage moves across the entire base of the platen.
Another ribbon drive includes a shaft extending through a support bracket secured to the printer carriage. One of the shafts is rotated in alternating directions as the carriage translates back and forth during printing and a friction wheel output is rotated in a single direction during printer translation. A gear and one-way bearing arrangement is operatively associated with the shaft for uni-directionally rotating the friction wheel output as the carriage moves back and forth.
U.S. Pat. No. 3,758,012, entitled CONTROL TENSION RIBBON CASSETTE and issued on Sept. 11, 1973 to Bonner et al discloses another form of ribbon drive. The drive disclosed therein includes a pressure roll mounted on a vertically oriented shaft and which is rotatably mounted on a cassette support portion of a printer carriage. A pair of toothed drive wheels or gears are secured to the shaft by oppositely operating one-way clutches. Flexible rack belts engage the drive wheels causing them to rotate and alternately drive the shaft uni-directionally.
Another ribbon drive which is similar to that disclosed in the aforementioned Bonner et al patent is shown in IBM Technical Disclosure Bulletin, to R. G. Cross Vol. 15, No. 7, page 2312 dated December 1972. A pair of hubs or spools are supported on a vertical drive shaft by oppositely operated one-way clutches. A rope or cord is wrapped around each of the hubs and around fixed pegs. The ends of the cord are fixed to the printer frame. Due to the direction of wrap of the rope or cord about both hubs, the shaft is driven in one direction as a print head moves in a back and forth manner.
The prior systems suffer from various problems relating to weight, cost and space requirement problems. The prior systems employing one or more rack belts require that special steps be taken to maintain the belt in driving engagement with the toothed wheel or gear. The same problems are experienced with the cord type of device since it must be stretched or maintained in tension to insure that the driving relationship is maintained between the cord and the bearing supported hubs.
A need, therefore, exists for a drive system for a carriage mounted ink ribbon cartridge having the capability of uni-directionally driving the ribbon while the carriage translates in both a forward and reverse direction and whereby the problems heretofore experienced are substantially alleviated.